Neutrophil responses to stimuli in vitro can be modulated by surface contact as well as by a number of environmental molecules. Neutrophil function appears to be influenced in vivo during trauma or sepsis and in some cases in postoperative conditions. Depending upon the conditions, the stimulus, and the modulator, these interactions have been reported to enhance or diminish free radical production and degranulation. This modulation has profound implications for our understanding of the roles that neutrophils play in inflammatory tissue injury. The biochemical basis of this modulation is not understood and could occur at any of three levels of cell activation: 1) stimulus- receptor dynamics, 2) the coupling of activated receptor (LR*) to the generation of cell signals and the regulation of cell signals, or 3) the regulation of cell responses (as a result either of topological redistribution of the participating components or of biochemical control). We have recently extended our technical capabilities to include the analysis and control of ligand-receptor dynamics, the analysis of intracellular signals, and the analysis of responses, all in real-time for adherent as well as suspension cells. We will combine these real-time measurements with analysis of the biochemistry of adherent and suspension cells in order to identify those features of the activation sequence which are influenced by surface contact or by environment modulators. We will vary the stimulus, the modulator and the nature of the surface to mimic vascular and/or tissue elements. These investigations will therefore begin to define the surface requirements, the stimulus requirements and the environmental factors for modulation of function. These studies will permit for the first time a high resolution, real-time analysis of ligand-receptor dynamics in adherent and suspension cells and permit a quantitative molecular analysis for describing the locus of functional modulation.